Assertion-Based Encapsulation, Object Invariants and Simulations

Abstract. Difficulties in reasoning about functional correctness and relational properties of object-oriented programs are reviewed. An approach using auxiliary state is briefly described, with emphasis on the author's work. Some near term challenges are sketched.Formal verification depends on scientific theories of programming, which answer questions such as these: What are good models of computational behavior? What behavioral properties of components are needed for modular reasoning about a composed system? How can such properties be specified and a component be verified, or even derived from its specification? How can a program and justification of its correctness be revised in accord with small revision of its specification? Such questions have well developed answers that are adequate for small programs under strong simplifying assumptions. But many useful programs are quite large and built from complicated components that violate simplifying assumptions.The longstanding challenge of compositional reasoning remains substantially unsolved. Object-oriented programs pose several challenges that are the focus of my recent research, in which auxiliary state is being used to specify encapsulation boundaries and disciplined interdependence. Section 2, explains the approach, accomplishments, and challenges in terms of invariants for shared mutable objects. Section 3 addresses relational properties including data refinement and secure information flow. This line of research has been carried out for Java-like programming languages; I argue in Section 1 for the importance of such languages. Some additional challenges pertinent to objectoriented programming, but not tied to the main theme, are discussed in Section 4. A detailed tutorial on the state-based approach to encapsulation advocated here appears elsewhere [33].Several near-term challenges (1-5 years) are presented here in the setting of sequential object-oriented programs. Because the approach taken here is based on the use of assertions, it is also quite relevant to verification of concurrent object-oriented programs and low level imperative code.

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Assertion-Based Encapsulation, Object Invariants and Simulations

Cited by 6 publications

References 38 publications

Modular Specification of Encapsulated Object-Oriented Components

Modular Specification of Encapsulated Object-Oriented Components

Smallfoot: Modular Automatic Assertion Checking with Separation Logic

Modular Reasoning in Object-Oriented Programming

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